"The greenhouse gas hypothesis – [...] – underpins a complex modelling exercise which tries to reproduce the way that global climate will develop over the 21st century and beyond.

The problem is that, just like complex financial derivatives, no-one really knows how the world's weather systems interact and evolve with time. Summer Arctic sea ice has been melting to a greater extent in recent years than was the case in the latter half of the 20th century, but is this due primarily to rising average temperatures driven by the additional radiative forcing provided by small increase in carbon dioxide, or to changes in winds and ocean currents, the ultimate drivers of which are not understood? Are patterns of drought and flood reflecting normal long-term cycles, or are they mainly influenced by an increase in the greenhouse effect? No-one knows for sure.

Even more importantly, climatologists are unable to understand enough about the formation and extent of different types of clouds to say whether they are having a net positive or negative effect on global temperatures. This may sound like a detail, but when a few percent difference in cloud cover can more than compensate for any carbon dioxide-driven temperature increase, it is a key factor. And yet complex computer models are being built on the belief that the world's climate system is sufficiently well understood not just to project its development many years into the future, but also to base on these projections policies which could force major changes to society. A complex model, based on dubious assumptions and poorly understood by those using it: sounds a bit like financial derivatives.

[...]

When it comes to climate, the official message is that temperatures are continuing to rise as models predict, with short-term influences such as La Niña affecting the actual figures year by year. Indeed, much of the media, fed the stories by activist scientists, is still willing to ramp up concerns about the speed of change being even faster than predicted (or, in IPCC-speak, projected). But the reality is that we have now had ten years without a rise in average temperatures. 2008 is being touted as the tenth warmest year on record. While this is factually correct, it is a misleading statistic, since there has been no upward trend in temperature over the last decade.

The IPCC tells us still to expect renewed warming in coming years. Other scientists point to the very quiet phase the Sun is entering, historically correlated with lower than average temperatures. Whatever may turn out to be the case, it is clearly impossible to project climatic changes with any realistic degree of certainty."

"How did the UN IPCC reports become the gold standard for documenting global warming if there are so many doubters? Because non-scientist policy-makers have the final say on what scientific conclusions and policies are included and UN claims of scientific support are highly exaggerated.

For example, the UN claimed 2,500 scientists supported its key claim that human-generated greenhouse gases are the primary cause of global warming. But those 2,500 weren't asked to support it--they were only asked to review it. Only 62 completed the review, and 55 had serious concerns, leaving a total of seven to support the science that is the basis of the IPCC climate-change policy."

"Anyone who goes around and says that carbon dioxide is responsible for most of the warming of the 20th century hasn't look at the basic numbers."Patrick Michaels - Ph.D. Ecological Climatology, Professor of Environmental Sciences, U. of Virginia

“We have 25 or so years invested in the work. Why should I make the data available to you, when your aim is to try and find something wrong with it.”Phil Jones, Professor in the School of Environmental Sciences at University of East Anglia, to Steve McIntyre